The present invention relates to sheet feeding apparatus and in particular to an adjustable sheet cassette capable of housing stacks of sheets or similar materials of different sizes.
In a particular application, the adjustable sheet cassette of the present invention has utility as a supply of stacked sheets in automatic printing apparatus such as reproducing apparatus including copiers, and electronic printers. Typically, in these devices, individual sheets of copy paper are separately fed through the copier and processed one at a time. In this process, it is convenient to have a supply stack of sheets from which to feed the individual sheets. Modern day business desires require that a copier or printer be capable of faithfully reproducing original documents of various sizes or configurations on various types of copy stock. To facilitate this operational flexibility, it has been customary to provide a supply of cut sheets in a cassette-type form. These paper sheet cassettes may be designed for a single fixed size of paper in which case they are only used for storing sheets of that size in the printing apparatus. Alternatively, adjustable cassettes may be designed to enable customer adjustment of the cassette for a variety of different sheet sizes. With the fixed size cassette if a printing operation is to be performed to obtain prints on a copy sheet size of a size other than that which is in the fixed cassette, the cassette must be removed from the machine and replaced with another cassette of a different fixed size to enable the operation to be completed. Similarly, with a adjustable adjustable cassette, if the size of the paper in the cassette is unsuitable for a particular printing operation, the copy sheets should be removed and replaced with the appropriate size copy sheets for that particular printing operation.
As a result of the use of different size copy sheets for different printing operations, it is becoming more customary to include a plurality of copy sheet sources in the printing apparatus which may be of different sizes from which the apparatus may automatically draw its copy sheet supply to perform any particular printing operation depending upon the size of the printing sheet desired. With such business printing desires, it becomes necessary that the printing apparatus know the size of the paper in each sheet supply location or cassette as soon as the cassette is inserted into the printing machine. There are several reasons why an automatic printing machine would require this information. For example, it enables the printing machine to automatically display the copy sheet size on the control panel to tell an operator a particular job can be run with the copy sheet size or to replace the copy sheet size. If the display does not automatically tell the operator, then the operator must gain access to the copy sheet supply to visually determine the size of the copy sheet supply. In addition, and with increasing sophistication in alternative capabilities in automatic printing machines, knowing the size of the copy sheets in any of the copy sheet supply locations in the automatic printing machine enables the automatic printing apparatus to select the appropriate size paper for size-to-size, automatic reduction and/or automatic enlargement of an original that may be placed on a copying platen. In addition, in some apparatus, the document feeder or sensors in the platen cover are capable of measuring the size of the document placed upon the imaging platen and selecting the correct size paper atomatically. If a copy sheet cassette is in the automatic printing machine and no size of the copy sheet in that cassette is determinable by the machine, the machine does not know if it has the appropriate size copy paper to match the size of the document being reproduced. Knowing the size of the copy sheets in each of the copy supply stations in an automatic printing machine enables the machine to automatically switch the sheet supplies thereby enabling, for example, in a long run of the same size copy paper, loading the same size paper in two sheet supply cassettes and when one supply is depleted, automatically switching to the other supply while the operator reloads the first supply. In addition in the automatic reduction and enlargement modes of operation, the automatic printing apparatus reads the size of the document and knows the degree of magnification desired by the operator. Knowing the size of the copy sheets in each of the copy supply stations enables the controller of the machine to calculate the closest paper size for the printing operation. Furthermore, if the automatic printing apparatus does not not know the size of the paper in the paper supply cassette and the apparatus is capable of scanning an original document placed on the imaging platen up to say 17" and only an 11" document is being copied, the scanning system does not known where to stop its scanning operation but rather scans the entire platen to capture the entire image. In addition to being inefficient in reducing the overall copy rate, this requires the use of more toner and more wear and tear on the machine. Accordingly, if the automatic printing apparatus can not automatically determine the copy sheet size, an operability difficulty is created in that the operator must gain access to the sheet supply in the apparatus to ensure that any particular printing operation may be performed. Thus by knowing the size of the copy sheets available in the printing apparatus, the printing apparatus can operate much more efficiently.
In prior art printing apparatus using sheet cassettes, several different techniques have been previously employed. Typically, for a fixed size sheet cassette such feature on the front of the cassette such as a rib, spring, magnet or button interacts with a bank of three or four sensors inside the copier to identify the size of the paper in the cassette. For customer adjustable cassettes, two different techniques have been used. In one, appropriate switches, wiring plugs, etc. are mounted into the cassette which after it is loaded into the automatic printing machine the operator must connect an electrical plug into the appropriate socket on the body of the automatic printing machine. This involves a complex operability difficulty and in addition is substantially more expensive than the fixed cassette approach. An additional technique used with the adjustable cassettes has been the use of the existing size sensing switches in the printing apparatus to have identified the cassette only as an adjustable cassette without identifying the size of the paper loaded. With this technique, the paper size in such a cassette will read "other" on the display panel on the control panel of the apparatus. While this technique has the advantage of lower cost, because the paper size is not known it tends to be useful only for unusual sizes of paper. In addition with this technique, the above-described automatic size, for size, reduction, enlargement and auto tray switching features must be disabled. As a result, customers typically purchase several fixed size cassettes for the common sizes of copy sheets that they will be using as well as an adjustable cassette for the miscellaneous odd sizes. This results in a large number of cassettes creating a storage problem as well as additional cost to the customer. The present invention is directed to a technique for identifying sheet sizes in an adjustable cassette by using switches which may already exist in the automatic printing machine and without requiring any switches, wires, plugs, etc. on the cassette itself which have to be plugged into the machine.